I am just starting to use XML within SQL Server 2008. I have the data in the XML, but I am having a hard time finding good examples of querying the data. Can someone point me to a good place to start? For example, I would want to find all rows within SQL server that contain a certain criteria within the XML like all rows where the XML contains an altitude > 10000.

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You can use the .value XML function to extract a given value from your XML field, based on a XPath expression (here: /root/altitude). You also need to define what type you're expecting to get back (possibly based on an XML schema), and this really gives you a value of that type which you can then use normally in any SQL statement and expression.

+1 for including a reference that does offer a few examples. Not sure who gave you a -1, but I agree that for real answers the OP should have included a specific example of what was wanted.
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Jon PetersonNov 21 '13 at 21:46

Generally you would use .exist() method if you want to find rows that match some xml criteria but don't need to return the xml document. This allows an optimized usage of the xml index (if you created one), whereas the engine has to touch the actual xml instance in most other cases.